EXPERIMENTAL-EVIDENCE FOR A LARGE COLLINEAR ELECTRIC-FIELD GRADIENT OF IR IN HCP-CO

Measurements of quadrapole-interaction-resolved NMR on oriented nuclei were performed on Ir-188 in a hcp-Co single crystal. The magnetic and electric hyperfine interaction frequencies were determined as functio n of the angle theta between the electronic magnetization (M) over rig ht arrow and the single crystal c axis, A large collinear electric fie ld gradient (CEFG) (principal axis parallel (M) over right arrow) was found, eq((c)) = -0.378(7) X 10(17) V/cm(2). Within the series of the 5d elements Ir, Pt, Au, and Hg this is exceptional: The experimental C EFG's of Pt, Au, and He in hcp-Co are at least similar to 2 orders of magnitude smaller and consistent with eq((c)) = 0.